Conventional evacuated blood collection tubes are known to be made with a rubber stopper penetrating the inside of the tube
intended to hold the vacuum and, at the same time prevent escape of the blood content.
Most of the health hazards inherent to these tubes stem from this single sealing concept. The high radial pressure of the stopper against the tube inner wall needed to hold the vacuum results in strong bouncing effect when the stopper is removed. Blood deposits adhering to the sealing surface are dispersed as slashes and aerosols.
Besides these blood dispersal phenomena, handling of these tubes expose the technicians to the risks of contact of the fingers with the large surface of the stopper smeared with blood.
Arrangements have been proposed as an attempt to minimize these problems. One of them consists in plastic caps covering these conventional vacuum tubes rubber bungs. These caps are set over the stopper head and their rigid skirt extends below the head, concentrically to the tube. A free space is provided between the tube wall and the cap to permit handling.
Although minimizing the risk of direct contact of fingers with the stopper walls, these caps did not resolve at all the blood dispersal phenomena, above described. It still is the same type of rubber bung that penetrates the tube to hold both the vacuum and blood so, the same effects of splashes and aerosols are produced which, the open end of the plastic cap totally fails to entrap. Systems cf this type have been described in literature.
Another arrangement presents a stopper made with a rubber skirt fitting over the neck of the tube, and integral with the skirt a plug that penetrates the tube. The sealing function is performed by two separate means mostly, the plug for the blood content and the upper cylindrical sealing portion for vacuum. These two sealing means are separated by an annular recess surrounding the central plug.
The stopper is movable outwardly on the tube from a sealing position to a venting position in which grooves or similar recesses having major axial components communicate the interior of the tube with the exterior (see FIGS. 1 and 2 of European patent No. 0022765). Although this system has improved handling of vacuum tubes, it still presents two major limitations. On the one hand, when the technician restoppers the tube, there is no mechanism which guarantees that the stopper plug is fully engaged inside the tube in the sealing position. The blind skirt fitting over the tube occults the position of the tube rim in relation to the central plug. As a consequence of this lack of visual control, it happens in routine use that the plug being partly engaged only or not engaged in the tube, blood spillage occurs unconspicuously within the system compromising the high standard of hygiene required today by laboratories.
A clenching mechanism would be required to achieve systematic guidance to the complete sealing position.
On the other hand, the pressure of the skirt wall around the tube neck outer wall tends to weaken over the time, due to the stretching condition of the stopper over the tube and to the deformability of the rubber material. As a consequence, vacuum may be lost.